This invention relates in general to universal joints and in particular to an improved structure for a constant velocity type of universal joint.
A universal joint is a mechanical coupling device which provides a rotational driving connection between two rotatable shafts, while permitting such shafts to be oriented at an angle relative to one another. Universal joints are commonly used in the drive train systems of vehicles. For example, a universal joint is commonly used to provide a rotational driving connection between a drive shaft rotatably driven by a vehicle engine and an input shaft connected to the vehicle axle assembly. This is because the drive shaft and the axle assembly input shaft are rarely co-axially aligned. To accommodate this non-alignment, while still providing a rotational driving connection, a universal joint is utilized therebetween.
Universal joints are commonly classified by their operating characteristics. One important operating characteristic relates to the relative angular velocities of the two shafts connected thereby. In a constant velocity type of universal joint, the instantaneous angular velocities of the two shafts are always equal, regardless of the angular orientation of the shafts. In a non-constant velocity type of universal joint, the instantaneous angular velocities of the two shafts vary with the angular orientation of the shafts (although the average angular velocities for a complete revolution are equal).
A typical constant velocity universal joint includes a cylindrical inner race connected to one of the shafts and a hollow cylindrical outer race connected to the other of the shafts. The outer surface of the inner race and the inner surface of the outer race have respective pluralities of grooves formed therein. The grooves extend linearly, having generally semi-circular cross sectional shapes. Each groove formed in the outer surface of the inner race is associated with a corresponding groove formed in the inner surface of the outer race. A ball is disposed in each of the associated pairs of grooves. The balls provide a driving connection between the inner and outer races. A generally hollow cylindrical cage is typically provided between the inner and outer races for retaining the balls in the grooves. The cage has circumferentially extending inner and outer surfaces and a plurality of openings formed therethrough for receiving and retaining the balls.
In one known type of constant velocity joint, the grooves formed in the outer surface of the inner race are oriented so as to be alternately inclined relative to the rotational axis of the joint. Similarly, the grooves formed in the inner surface of the outer race are also alternately inclined relative to the rotational axis of the joint. For each pair of associated inner and outer race grooves, the inner race groove is inclined in one direction relative to the rotational axis of the joint, while the outer race groove is inclined in the opposite direction. Thus, this type of joint is commonly referred to as a cross groove constant velocity joint or, more simply, a cross groove joint.
Most cross groove joints permit the inner race and its associated shaft to move axially relative to the outer race and its associated shaft. Thus, the center point of the inner race (i.e., the point defined by the intersection of the axis of rotation of the inner race with a perpendicular plane bisecting the inner race) can be axially displaced from center point of the outer race. This axial displacement is desirable because it permits the two shafts to move axially relative to one another during operation.
However, it has been found that the ability of the cross groove joint to accommodate angular movement between the two shafts is inversely related to the ability of the joint to accommodate axial movement therebetween. In other words, as the center points of the two races are displaced at a greater distance, the joint can accommodate a lesser amount of relative angular movement therebetween. For example, a typical joint may accommodate an angular orientation of 18.0.degree. between the two shafts when the center points of the inner and outer races are displaced by 14.7 mm. The same joint will accommodate only an angular orientation of 6.0.degree. when such center points are displaced by 24.0 mm.
This inverse relationship between the angular movement and axial displacement of the inner and outer races is a result of the internal structure of the cross groove joint. Specifically, it has been found that when the center point of the inner race is axially displaced from the center point of the outer race, angular movement of the inner race causes the center point thereof to move laterally with respect to the center point of the outer race. As a result, the center point of the inner race moves out of alignment with the axis of rotation of the outer race. Consequently, angular movement of the inner race causes the outer surface thereof to engage the inner surface of the cage, preventing further angular movement. The ratio of this lateral movement of the center point of the inner race to the amount of angular movement increases with the amount of axial displacement of the center points of the inner and outer races. Thus, as the center points of the inner and outer races are displaced at a greater distance, the joint can accommodate a lesser amount of relative angular movement therebetween.
It is known to design cross groove joints to meet the specific angular movement and axial displacement requirements of a particular application. This is usually accomplished by enlarging the entire joint structure to accommodate both greater angular movements and axial displacements than would otherwise be available. However, it would be desirable to provide an improved structure for a cross groove joint which can accommodate both greater angular movements and axial displacements than previously attainable without increasing the overall size thereof.